Can we go back to preventing users from Creating Globally Visible Distribution Lists as a default? Yes, I know there are workarounds, but it would just be better if this never was allowed to begin with.

Voting

Users can manage Distribution groups, but can only add members who have an AD object.

For example : Add a second multi-value attribute (eg externalMembers) and a permissions mask to provide the ability for an administrator to allow certain DGs to have a secondary list of external SMTP addresses.